טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentCherkes Ira
SubjectElectron Relaxation in Quantum Dots by the Interatomic
Coulombic Decay Mechanism
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisor Professor Emeritus Nimrod Moiseyev
Full Thesis textFull thesis text - English Version


Abstract

Electron relaxation in quantum dot (QD) systems has a significant impact on QD optoelectronic devices such as lasers, photodetectors and solar cells. Several different fundamental mechanisms are known. One such relaxation mechanism is photon emission, which is on the timescale of nanoseconds. Another relaxation mechanism is due to a strong interaction with longitudinal optical phonons, which is on the timescale of picoseconds. In addition a much faster mechanism, on the timescale of femtoseconds, is an intra-dot Auger relaxation.


In this work we propose another possible relaxation mechanism which is based on the interatomic Coulombic decay (ICD) mechanism first predicted  by Cederbaum and his coworkers in 1997 and which has been recently  observed in atomic Van der Waals clusters and in hydrogen-bonded molecular clusters. ICD is an inter-dot electron correlation effect. We show that the electron relaxation in a quantum dot dimer due to the ICD mechanism is on a femtoseconds timescale and occurs at a distance of tens of nanometers between the centers of the QDs. This mechanism enables us to design infrared photodetectors which are extremely efficient for ultra-weak radiation with a specific wavelength.


The energies and the lifetimes for the ICD process were calculated by using a Gaussian basis set. This is one of the most popular basis sets in chemistry. However, one of the questions is how the value of the exponents of the Gaussians are determined. In this work we also show how and why the well-known Gaussian even-tempered basis spans the Hilbert space evenly. This basis is thought to be chosen based mainly on empirical results. However, as shown here, it can also be deduced based on rigorous numerical grounds using a Gram-Schmidt orthogonalization procedure.